This invention relates to oil compositions, primarily to fuel oil compositions, and more especially to fuel oil compositions susceptible to wax formation at low temperatures, and to additive compositions for such fuel oil compositions.
Heating oils and other distillate petroleum fuels, for example, diesel fuels, contain alkanes that at low temperature tend to precipitate as large crystals of wax in such a way as to form a gel structure which causes the fuel to lose its ability to flow. The lowest temperature at which the fuel will still flow is known as the pour point.
As the temperature of the fuel falls and approaches the pour point, difficulties arise in transporting the fuel through lines and pumps. Further, the wax crystals tend to plug fuel lines, screens, and filters at temperatures above the pour point. These problems are well recognized in the art, and various additives have been proposed, many of which are in commercial use, for depressing the pour point of fuel oils. Similarly, other additives have been proposed and are in commercial use for reducing the size and changing the shape of the wax crystals that do form. Smaller size crystals are desirable since they are less likely to clog a filter; certain additives inhibit the wax from crystallizing as platelets and cause it to adopt an acicular habit, the resulting needles being more likely to pass through a filter than are platelets. The additives may also have the effect of retaining in suspension in the fuel the crystals that have formed, the resulting reduced settling also assisting in prevention of blockages.
Effective wax crystal modification (as measured by CFPP and other operability tests, as well as simulated and field performance) may be achieved by ethylene-vinyl acetate or propionate copolymer (EVAC or EVPC)-based flow improvers.
In EP-A-45342 is described a cold flow additive, based on an EVAC modified by esterification with 2-ethylhexanoic, acrylic, and phthalic acids.
In xe2x80x9cWissenschaft und Technikxe2x80x9d 42(6), 238 (1989), M. Ratsch and M. Gebauer describe cold flow additives including an EVAC esterified with, inter alia, n-hexanoic acid.
In U.S. Pat. No. 3,961,916, middle distillate flow improvers are described which comprise a wax growth arrestor and a nucleating agent, the former being preferably a lower molecular weight ethylene-vinyl ester copolymer with a higher ester content, the latter preferably a higher molecular weight copolymer with a lower ester content, the esters preferably, but not necessarily, both being vinyl acetate.
In DE-AS-2407158, middle distillate flow improvers are described, comprising a mixture of low molecular weight ethylene-vinyl ester and ethylene-acrylic acid ester copolymers, both containing at least 40 mole per cent of the ester component.
The present invention is concerned to provide an oil, especially a fuel oil, additive effective to improve low temperature flow of the oil, and is based on the observation that a composition comprising at least two different copolymers of ethylene with an unsaturated ester, or a composition comprising a copolymer of ethylene with at least two different types of unsaturated ester-derivable units, is an effective cold flow improver having advantages over previously proposed compositions.
In a first aspect, the present invention provides a composition comprising
(a) an oil soluble ethylene copolymer having, in addition to units derived from ethylene, units of the formula
xe2x80x94CH2xe2x80x94CRR1xe2x80x94xe2x80x83xe2x80x83I
and units of the formula
xe2x80x94CH2xe2x80x94CRR2xe2x80x94xe2x80x83xe2x80x83II
the total molar proportion of units of the formulae I and II in the copolymer being less than lot, wherein each R independently represents H or CH3, and each R1 and R2 independently represents a group of the formula COOR3 or OOCR3, wherein each R3 independently represents a hydrocarbyl group, provided that the units of the formula I are different from the units of the formula II, or (b) comprising
(i) an oil-soluble ethylene copolymer having, in addition to units derived from ethylene, less than 10 molar per cent of units of the formula
xe2x80x94CH2xe2x80x94CRR1xe2x80x94xe2x80x83xe2x80x83I
and (ii) an oil-soluble ethylene copolymer having, in addition to units derived from ethylene, less than 10 molar per cent of units of the formula
xe2x80x94CH2xe2x80x94CRR2xe2x80x94xe2x80x83xe2x80x83II
wherein R, R1, and R2 have the meanings given above, provided that copolymer (i) differs from copolymer (ii). Advantageously, R represents H.
As used in this specification the term xe2x80x9chydrocarbylxe2x80x9d refers to a group having a carbon atom directly attached to the rest of the molecule and having a hydrocarbon or predominantly hydrocarbon character. Among these, there may be mentioned hydrocarbon groups, including aliphatic, (e.g., alkyl or alkenyl), alicyclic (e.g., cycloalkyl or cycloalkenyl), aromatic, aliphatic and alicyclic-substituted aromatic, and aromatic-substituted aliphatic and alicyclic groups. Aliphatic groups are advantageously saturated. These groups may contain non-hydrocarbon substituents provided their presence does not alter the predominantly hydrocarbon character of the group. Examples include keto, halo, hydroxy, nitro, cyano, alkoxy and acyl. If the hydrocarbyl group is substituted, a single (mono) substituent is preferred. Examples of substituted hydrocarbyl groups include 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl, 2-ketopropyl, ethoxyethyl, and propoxypropyl. The groups may also or alternatively contain atoms other than carbon in a chain or ring otherwise composed of carbon atoms. Suitable hetero atoms include, for example, nitrogen, sulfur, and, preferably, oxygen. Advantageously, the hydrocarbyl group contains at most 30, preferably at most 15, more preferably at most 10 and most preferably at most 8, carbon atoms.
Advantageously R3 represents an alkenyl or as indicated above, preferably, an alkyl group, which is advantageously linear. If the alkyl or alkenyl group is branched, for example, as in the 2-ethylhexyl group, the xcex1-carbon atom is advantageously part of a methylene group. Advantageously, the alkyl or alkenyl group contains up to 30 carbon atoms, preferably from 1 (2 in the case of alkenyy) to 14 carbon atoms, and more preferably from 4 to 10 carbon atoms. As examples of alkyl or alkenyl groups there may be mentioned propyl, n-butyl, iso-butyl, and isomers, preferably the linear isomers, of pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl and icosyl, and their corresponding alkenyl, advantageously alk-omega-enyl, radicals. When R1 and/or R2 are of the formula OOCR3, R3 most preferably represents propyl, butyl, or pentyl, and as indicated above, advantageously the linear isomer.
As cycloalkyl, alkaryl and aryl radicals, there may be mentioned, for example, cyclohexyl, benzyl and phenyl.
The copolymer or copolymers may also contain units of formulae other than those mentioned above, for example units of the formula
xe2x80x94CH2xe2x80x94CRR4xe2x80x94xe2x80x83xe2x80x83II
where R4 represents xe2x80x94OH, or of the formula
xe2x80x94CCH3(CH2R5)xe2x80x94CHR6xe2x80x94xe2x80x83xe2x80x83IV
where R5 and R6 each independently represent hydrogen or an alkyl group with up to 4 carbon atoms, the units IV advantageously being derived from isobutylene, 2-methylbut-2-ene or 2-methylpent-2-ene.
Units of the formula I or II may be terminal units but are advantageously internal units. Advantageously, units of the formula xe2x80x94CRR1xe2x80x94CH2xe2x80x94 and xe2x80x94CRR2xe2x80x94CH2xe2x80x94 represent less than 7.5, preferably from 0.3 to 7.5, and most preferably from 3.5 to 7.0, mole per cent of the polymer.
The copolymer (a) and each of copolymers b(i) and (ii) advantageously have a number average molecular weight, as measured by gel permeation chromatography, of up to 20,000, advantageously up to 15,000, more advantageously in the range of 1,200 to 10,000, preferably 3,000 to 10,000 and most preferably about 5,000. The preferred number average molecular weight will depend to some extent on the number of carbon atoms in R3, the higher that number the higher the preferred molecular weight within the range above. Advantageously, the number average molecular weights of the polymers b(i) and b(ii) differ by at most 2000, more especially by at most 1000.
Polymers in which R1 or R2 represents OOCR3 are preferred and more preferably both R1 and R2 both represent OOCR3.
It is within the scope of the invention to use both a polymer (a) and the mixture of polymers (b) in the same additive composition. It is also within the scope of the invention to employ a polymer (a) having more than two different units of types I and II, or mixtures of two or more polymers (a). When employing the mixture of polymers (b), units I in polymer (b)i are advantageously different from units II in polymer (b)ii, but it is also within the scope of the invention to employ a mixture of copolymers in which units I and II are the same, provided that the polymers differ in at least one respect, for example, proportion of units I and II in the polymer, the molecular weight, or the molecular weight distribution, of the polymer, the linearity of the polymer, or the presence of other units in the polymer.
The invention also provides an oil containing the additive composition, and an additive concentrate comprising the additive composition in admixture with an oil or a solvent miscible with the oil. The invention further provides the use of the additive composition to improve the low temperature properties of an oil. The oil may be a crude oil, i.e. oil obtained directly from drilling and before refining, the compositions of this invention being suitable for use as flow improvers therein.
The oil may be a lubricating oil, which may be an animal, vegetable or mineral oil, such, for example, as petroleum oil fractions ranging from naphthas or spindle oil to SAE 30, 40 or 50 lubricating oil grades, castor oil, fish oils or oxidized mineral oil. Such an oil may contain additives depending on its intended use; examples are viscosity index improvers such as ethylene-propylene copolymers, succinic acid based dispersants, metal containing dispersant additives and zinc dialkyl-dithiophosphate antiwear additives. The compositions of this invention may be suitable for use in lubricating oils as flow improvers, pour point depressants or dewaxing aids.
The oil may be a fuel oil, especially a middle distillate fuel oil. Such distillate fuel oils generally boil within the range of from 110xc2x0 C. to 500xc2x0 C., e.g. 150xc2x0 to 400xc2x0 C. The fuel oil may comprise atmospheric distillate or vacuum distillate, or cracked gas oil or a blend in any proportion of straight run and thermally and/or catalytically cracked distillates. The most common petroleum distillate fuels are kerosene, jet fuels, diesel fuels, heating oils and heavy fuel oils. The heating oil may be a straight atmospheric distillate, or it may contain minor amounts, e.g. up to 35 wt %, of vacuum gas oil or cracked gas oils or of both. The above-mentioned low temperature flow problem is most usually encountered with diesel fuels and with heating oils. The invention is also applicable to vegetable-based fuel oils, for example rape seed oil.
The additive or additives should preferably be soluble in the oil to the extent of at least 1000 ppm by weight per weight of oil at ambient temperature. However, at least some of the additive may come out of solution near the cloud point of the oil and function to modify the wax crystals that form.
In the composition (b) according to the invention, polymer (i) is advantageously an ethylene-vinyl acetate or propionate copolymer. Advantageously, the linearity of the polymer as expressed by the number of methyl groups per 100 methylene units, as measured by proton NMR, is from 1 to 15.
The copolymers, especially the ethylene-vinyl acetate or propionate copolymer may be made by any of the methods known in the art, e.g., by solution polymerization with free radical initiation, or by high pressure polymerization, conveniently carried out in an autoclave or a tubular reactor.
Alternatively, the copolymer may be made by saponification and re-esterification of an ethylene-vinyl acetate or propionate, or an ethylene-methyl or ethyl (meth)acrylate, copolymer.
A further method of making the copolymer is by transesterification, provided that the entering acid or alcohol is less volatile than that being removed.
If desired all, or substantially all, existing ester groups may be hydrolysed and completely replaced by the desired chain substituents. Alternatively, a proportion only may be hydrolysed, so that the resulting polymer contains, for example, acetate side chains and chains of longer length.
Where a copolymer (a) is being made, a mixture of ester monomer (where the polymer is being made directly) or of acid or alcohol reactants (where re-esterification or transesterification is being effected) is used in appropriate proportions, taking any differences in reactivity of the materials into account.
In embodiment (a) of the invention, units I and units II are preferably present in a molar ratio in the range of 2:98 to 98:2, advantageously 5:95 to 95:5, more especially from 1:10 to 10:1. In embodiment (b) polymers containing units I and units II are advantageously present in a weight ratio of from 10:1 to 1:10, preferably from 3:1 to 1:3, and more preferably in a ratio of about 1:1.
The additive composition and the oil composition may contain other additives for improving low temperature and/or other properties, many of which are in use in the art or known from the literature.
For example, the composition may also contain a further ethylene-vinyl ester copolymer. As mentioned above, with reference to U.S. Pat. No. 3,961,916, flow improver compositions may comprise a wax growth arrestor and a nucleating agent. Without wishing to be bound by any theory, the applicants believe that the additive compositions of the present invention act primarily as nucleators, and benefit from the addition of arrestors, e.g., an ethylene-vinyl ester, especially acetate, having a number average molecular weight in the range of at most 14,000, and a vinyl ester content of 7.5 to 35 molar per cent, advantageously an ester content higher, and preferably at least 2, more preferably at least 3, molar per cent higher, than that of any ester in the additive composition as defined above.
The additive composition may also comprise a comb polymer. Such polymers are discussed in xe2x80x9cComb-Like Polymers. Structure and Propertiesxe2x80x9d, N. A. Platxc3xa9 and V. P. Shibaev, J. Poly. Sci. Macromolecular Revs., 8, p 117 to 253 (1974).
Advantageously, the comb polymer is a homopolymer having, or a copolymer at least 25 and preferably at least 40, more preferably at least 50, molar per cent of the units of which have, side chains containing at least 6, and preferably at least 10, atoms.
As examples of preferred comb polymers there may be mentioned those of the general formula 
wherein D=R11 COOR11, OCOR11, R12COOR11, or OR11,
E=H, CH3, D, or R12,
G=H or D
J=H, R12, R12COOR11, or an aryl or heterocyclic group,
K=H, COOR12, OCOR12, OR12, or COOH,
L=H, R12, COOR12, OCOR12, COOH, or aryl,
R11xe2x89xa7C10 hydrocarbyl,
R12xe2x89xa7C1 hydrocarbyl,
and m and n represent mole ratios, m being within the range of from 1.0 to 0.4, n being in the range of from 0 to 0.6. R11 advantageously represents a hydrocarbyl group with from 10 to 30 carbon atoms, while R12 advantageously represents a hydrocarbyl group with from 1 to 30 carbon atoms.
The comb polymer may contain units derived from other monomers if desired or required. It is within the scope of the invention to include two or more different comb copolymers.
These comb polymers may be copolymers of maleic anhydride or fumaric acid and another ethylenically unsaturated monomer, e.g., an xcex1-olefin or an unsaturated ester, for example, vinyl acetate. It is preferred but not essential that equimolar amounts of the comonomers be used although molar proportions in the range of 2 to 1 and 1 to 2 are suitable. Examples of olefins that may be copolymerized with e.g., maleic anhydride, include 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene.
The copolymer may be esterified by any suitable technique and although preferred it is not essential that the maleic anhydride or fumaric acid be at least 50% esterified. Examples of alcohols which may be used include n-decan-1-ol, n-dodecan-1-ol, n-tetradecan-1-ol, n-hexadecan-1-ol, and n-octadecan-1-ol. The alcohols may also include up to one methyl branch per chain, for example, 1-methylpentadecan-1-ol, 2-methyltridecan-1-ol. The alcohol may be a mixture of normal and single methyl branched alcohols. It is preferred to use pure alcohols rather than the commercially available alcohol mixtures but if mixtures are used the R12 refers to the average number of carbon atoms in the alkyl group; if alcohols that contain a branch at the 1 or 2 positions are used R12 refers to the straight chain backbone segment of the alcohol.
These comb polymers may especially be fumarate or itaconate polymers and copolymers such for example as those described in European Patent Applications 153176, 153177 and 225688, and WO 91/16407.
Particularly preferred fumarate comb polymers are copolymers of alkyl fumarates and vinyl acetate, in which the alkyl groups have from 12 to 20 carbon atoms, more especially polymers in which the alkyl groups have 14 carbon atoms or in which the alkyl groups are a mixture of C14/C16 alkyl groups, made, for example, by solution copolymerizing an equimolar mixture of fumaric acid and vinyl acetate and reacting the resulting copolymer with the alcohol or mixture of alcohols, which are preferably straight chain alcohols. When the mixture is used it is advantageously a 1:1 by weight mixture of normal C14 and C16 alcohols. Furthermore, mixtures of the C14 ester with the mixed C14/C16 ester may advantageously be used. In such mixtures, the ratio of C14 to C14/C16 is advantageously in the range of from 1:1 to 4:1, preferably 2:1 to 7:2, and most preferably about 3:1, by weight.
Other suitable comb polymers are the polymers and copolymers of xcex1-olefins and esterified copolymers of styrene and maleic anhydride, and esterified copolymers of styrene and fumaric acid; mixtures of two or more comb polymers may be used in accordance with the invention and, as indicated above, such use may be advantageous.
The additive composition may also comprise polar nitrogen compounds, for example those described in U.S. Pat. No. 4,211,534, especially an amide-amine salt of phthalic anhydride with two molar proportions of hydrogenated tallow amine, or the corresponding amidexe2x80x94amine salt of ortho-sulphobenzoic anhydride.
The additive composition of the invention may also comprise a copolymer of ethylene and at least one xcex1-olefin, having a number average molecular weight of at least 30,000. Preferably the xcex1-olefin has at most 20 carbon atoms. Examples of such olefins are propylene, 1-butene, isobutene, n-octene-1, isooctene-1, n-decene-1, and n-dodecene-1. The copolymer may also comprise small amounts, e.g, up to 10% by weight of other copolymerizable monomers, for example olefins other than xcex1-olefins, and non-conjugated dienes. The preferred copolymer is an ethylene-propylene copolymer. It is within the scope of the invention to include two or more different ethylene-xcex1-olefin copolymers of this type.
The number average molecular weight of the ethylene-xcex1-olefin copolymer is, as indicated above, at least 30,000, as measured by gel permeation chromatography (GPC) relative to polystyrene standards, advantageously at least 60,000 and preferably at least 80,000. Functionally no upper limit arises but difficulties of mixing result from increased viscosity at molecular weights above about 150,000, and preferred molecular weight ranges are from 60,000 and 80,000 to 120,000.
Advantageously, the copolymer has a molar ethylene content between 50 and 85 per cent. More advantageously, the ethylene content is within the range of from 57 to 80%, and preferably it is in the range from 58 to 73%; more preferably from 62 to 71%, and most preferably 65 to 70%.
Preferred ethylene-a-olefin copolymers are ethylene-propylene copolymers with a molar ethylene content of from 62 to 71% and a number average molecular weight in the range 60,000 to 120,000, especially preferred copolymers are ethylene-propylene copolymers with an ethylene content of from 62 to 71% and a molecular weight from 80,000 to 100,000.
The copolymers may be prepared by any of the methods known in the art, for example using a Ziegler type catalyst. The polymers should be substantially amorphous, since highly crystalline polymers are relatively insoluble in fuel oil at low temperatures.
The additive composition may also comprise a further ethylene-xcex1-olefin copolymer, advantageously with a number average molecular weight of at most 7500, advantageously from 1,000 to 6,000, and preferably from 2,000 to 5,000, as measured by vapour phase osmometry. Appropriate xcex1-olefins are as given above, or styrene, with propylene again being preferred. Advantageously the ethylene content is from 60 to 77 molar per cent although for ethylene-propylene copolymers up-to 86 molar per cent by weight ethylene may be employed with advantage.
The composition may also comprise poly(ethylene glycol) esters, advantageously of fatty acids containing from 18 to 22 carbon atoms in the chain, especially when the fuel being treated lacks higher alkanes that act as wax crystallization nucleators.
In addition, the additive composition and the fuel oil composition may contain additives for other purposes, e.g., for reducing particulate emission or inhibiting colour and sediment formation during storage.
The fuel oil composition of the invention advantageously contains the additive of the invention, i.e., components (a) and (b) above, in a total proportion of 0.0005% to 1%, advantageously 0.001 to 0.1%, and preferably 0.04 to 0.06% by weight, based on the weight of fuel.